The airsacs in the lungs of mammals are stabilized by pulmonary surfactant, a complex mixture containing glycerophospholipids and specific surfactant proteins (SP) that is synthesized by type II epithelial cells in the alveolar lining (for review see text by Notter (Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000)). The mammalian lungs have a huge internal surface area of the order 1 m2/kg body weight at total lung capacity, and much of this surface is lined by a thin liquid film or “alveolar hypophase”. Surface tension forces at the extensive air-hypophase interface are a major contributor to the work of breathing. Pulmonary surfactant plays crucial roles in respiratory physiology by moderating these surface tension forces. Endogenous surfactant secreted by alveolar type II epithelial cells adsorbs at the air-hypophase interface and lowers and varies surface tension as a function of alveolar size during breathing. This regulation of surface tension reduces the work of breathing while stabilizing different sized alveoli against collapse and overdistension. It also leads to a smaller hydrostatic pressure driving force for edema fluid to move into the lung interstitium from the pulmonary capillaries. Functional pulmonary surfactant is necessary for life, and its deficiency or dysfunction is associated with severe impairments in respiratory function that can be lethal if not treated effectively.
A major disease where lung surfactant deficiency causes respiratory failure is the neonatal respiratory distress syndrome (“NRDS”), also called Hyaline Membrane Disease (“HMD”). NRDS is most prevalent in premature infants <32 weeks gestation (term=40 weeks in humans), but it can also occur in older premature infants of 32-36 weeks gestation. NRDS is caused by a deficiency of endogenous surfactant in the lungs of premature infants at birth (although elements of lung injury with acquired surfactant dysfunction can subsequently arise during its clinical course). The major clinical conditions associated with lung surfactant dysfunction are the syndromes of acute lung injury (“ALI”) and the acute respiratory distress syndrome (“ARDS”). ALI and ARDS are lethal manifestations of inflammatory lung injury that can result from multiple direct and indirect causes ranging from respiratory infection, gastric aspiration, meconium aspiration, blunt chest trauma with lung contusion, hyperoxia, near drowning, hypovolemic shock, bacterial sepsis, and many others (for review see Notter et al., editors, Lung Injury: Mechanisms, Pathophysiology and Therapy, Taylor Francis Group, Inc, Boca Raton (2005)). ALI/ARDS can affect patients of all ages from infants to adults, although different age groups vary somewhat in the etiology and specifics of disease. The American-European Consensus Committee in 1994 defined clinical ARDS more specifically as requiring an acute onset, bilateral infiltrates on frontal chest radiograph, a PaO2/FiO2 ratio 200 mmHg, and a pulmonary capillary wedge pressure mmHg (if measured) or no evidence of left atrial hypertension (Bernard et al., “The American-European Consensus Conference on ARDS: Definitions, Mechanisms, Relevant Outcomes, and Clinical Trial Coordination,” Am J Respir Crit Care Med 149:818-824 (1994)). The Consensus Committee defined ALI identically to ARDS except for a PaO2/FiO2 ratio 300 mmHg (Bernard et al., “The American-European Consensus Conference on ARDS: Definitions, Mechanisms, Relevant Outcomes, and Clinical Trial Coordination,”Am J Respir Crit Care Med 149:818-824 (1994)). ARDS affects 50,000 to 150,000 patients in the United States each year, and the incidence of ALI is estimated at 22-86 cases per 100,000 people per year. Both conditions have substantial mortality rates of 30-50% despite sophisticated intensive care (Bernard et al., “The American-European Consensus Conference on ARDS: Definitions, Mechanisms, Relevant Outcomes, and Clinical Trial Coordination,” Am J Respir Crit Care Med 149:818-824 (1994); Rubenfeld et al., “Incidence and Outcomes of Acute Lung Injury,” N Engl J Med 363:1685-1693 (2005); Hyers, “Prediction of Survival and Mortality in Patients With the Adult Respiratory Distress Syndrome,” New Horizons 1:466-470 (1993); Doyle et al., “Identification of Patients With Acute Lung Injury: Predictors of Mortality,” Am J Respir Crit Care Med 152:1818-1824 (1995); Krafft et al., “The Acute Respiratory Distress Syndrome; Definitions, Severity, and Clinical Outcome. An Analysis of 101 Clinical Investigations,” Intensive Care Med 22:519-529 (1996); Goss et al., “Incidence of Acute Lung Injury in the United States,” Crit Care Med 31:1607-1611 (2003)). Multiple studies have identified surfactant abnormalities in bronchoalveolar lavage (lung washings) from patients with ALI/ARDS (e.g., Petty et al., “Characteristics of Pulmonary Surfactant in Adult Respiratory Distress Syndrome Associated With Trauma and Shock,” Am Rev Respir Dis 115:531-536 (1977); Hallman et al., “Evidence of Lung Surfactant Abnormality in Respiratory Failure,” J Clin Invest 70:673-683 (1982); Seeger et al., “Surfactant Abnormalities and Adult Respiratory Failure,” Lung 168 (Suppl):891-902 (1990); Pison et al., “Surfactant Abnormalities in Patients With Respiratory Failure After Multiple Trauma,” Am Rev Respir Dis 140:1033-1039 (1989); Gregory et al., “Surfactant Chemical Composition and Biophysical Activity in Acute Respiratory Distress Syndrome,” J Clin Invest 88:1976-1981 (1991); Veldhuizen et al., “Pulmonary Surfactant Subfractions in Patients With the Acute Respiratory Distress Syndrome,” Am J Respir Crit Care Med 152:1867-1871 (1995); Griese, “Pulmonary Surfactant in Health and Human Lung Diseases: State of the Art,” Eur Respir J 13:1455-1476 (1999); Gunther et al., “Surfactant Alterations in Severe Pneumonia, Acute Respiratory Distress Syndrome, and Cardiogenic Lung Edema,” Am J Respir Crit Care Med 153:176-184 (1996)).
Surfactant dysfunction in ALI/ARDS occurs by several mechanisms including physical and chemical interactions with inhibitors in edema fluid or lung tissue (Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000); Notter et al., “Pulmonary Surfactant: Physical Chemistry, Physiology and Replacement,” Rev Chem Eng 13:1-118 (1997); Wang et al., “Surfactant Activity and Dysfunction in Lung Injury,” In: Notter et al., editors, Lung Injury: Mechanisms, Pathophysiology, and Therapy, Taylor Francis Group, Inc, Boca Raton, pp. 297-352 (2005)). To be optimally effective, exogenous surfactants used in treating ALI/ARDS and/or severe NRDS must have very high surface activity and resistance to biophysical inhibition and/or chemical degradation.
If endogenous surfactant is deficient or dysfunctional, it can in principle be treated by the delivery of active exogenous surface-active material to the alveoli by airway instillation or by other techniques such as aerosolization or nebulization. Exogenous surfactant therapy is intended to preserve lung function over the short term while the patient's lungs develop or recover the ability to produce and maintain adequate levels of endogenous surfactant. The utility of exogenous surfactant therapy with first-generation animal-derived clinical surfactant drugs to prevent or treat NRDS in premature infants is well documented (for review see: Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000); Soll, “Surfactant Therapy in The USA: Trials and Current Routines,” Biol Neonate 71:1-7 (1997); Soll et al., “Surfactant in the Prevention and Treatment of Respiratory Distress Syndrome,” In: New Therapies for Neonatal Respiratory Failure, Boynton et al., editors, Cambridge University Press, New York, pp. 49-80 (1994); Jobe, “Pulmonary Surfactant Therapy,” N Engl J Med 328:861-868 (1993)). Exogenous surfactant therapy is still under development for ALI/ARDS, but the existence of surfactant dysfunction in patients with this condition provides a clear conceptual rationale for the potential benefits of such therapy (Chess et al., “Surfactant Replacement Therapy in Lung Injury,” In: Lung Injury: Mechanisms, Pathophysiology, and Therapy, Notter et al., editors, Taylor Francis Group, Inc, Boca Raton, pp. 617-663 (2005); Raghavendran, et al., “Pharmacotherapy of Acute Lung Injury and Acute Respiratory Distress Syndrome,” Curr Med Chem 15:1911-1924 (2008); Willson et al., “Surfactant for Pediatric Acute Lung Injury,” Pediatr Clin N Am 55:545-575 (2008)).
Published research shows that current animal-derived clinical exogenous surfactants, e.g., Infasurf® (CLSE), Survanta®, and Curosurf®, are more active biophysically and physiologically than first-generation synthetic surfactants such as Exosurf® and ALEC (Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000); Soll, “Surfactant Therapy in The USA: Trials and Current Routines,” Biol Neonate 71:1-7 (1997); Soll et al., “Surfactant in the Prevention and Treatment of Respiratory Distress Syndrome,” In: New Therapies for Neonatal Respiratory Failure, Boynton et al., editors, Cambridge University Press, New York, pp. 49-80 (1994); Jobe, “Pulmonary Surfactant Therapy,” N Engl J Med 328:861-868 (1993)). These animal-derived clinical surfactants all contain one or both of the lung surfactant proteins (SP)-B and/or SP-C as essential ingredients (Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000).
However, synthetic lung surfactants manufactured under controlled conditions have significant potential advantages in purity, compositional reproducibility, activity reproducibility, quality-control, and manufacturing economy compared to animal-derived preparations. In addition, constituents in synthetic surfactants can incorporate special and useful molecular properties, such as resistance to degradation by phospholipases during inflammatory lung injury ((Notter, Lung Surfactants: Basic Science and Clinical Applications, Marcel Dekker, Inc, New York (2000); Wang et al., “Surface Activity of a Synthetic Lung Surfactant Containing a Phospholipase-resistant Phosphonolipid Analog of Dipalmitoyl Phosphatidylcholine,” Am J Physiol 285:L550-L559 (2003); Wang et al., “Activity and Inhibition Resistance of a Phospholipase-Resistant Synthetic Exogenous Surfactant in Excised Rat Lungs,” Am J Respir Cell Mol Biol 37:387-394 (2007)). Synthetic surfactants are also free from concerns about prion-caused diseases (e.g., bovine spongiform encephalitis) that are relevant for animal-derived surfactants, and synthetic surfactants are not subject to cultural or religious considerations that potentially affect bovine- or porcine-derived preparations.
Despite significant advances in recent years, there remains a need to identify improved synthetic SP-B peptides and SP-C peptides that show enhanced activity and/or stability, can be easily produced in pure form and in a cost-effective manner, and can be used to generate synthetic surfactant compositions having activity comparable to or better than the activities of commercially available animal-derived surfactants.
The present invention is directed to overcoming these and other deficiencies in the art.